feat: add get_quest_category endpoint

[irisdv]

Part of lfglabs-dev/starknet.quest#377

This PR adds a new endpoint get_quest_category which fetches a new collection called quest_categories with data to show customized meta tags for category pages in the front end.

QuestCategoryDocument {
    name: String,
    title: String,
    desc: String,
    img_url: String,
}